1. Field of the Invention
The invention relates to a hydraulic transaxle including a hydraulic motor for driving an axle, provided with a bypass valve bypassing between suction and delivery ports of the hydraulic motor, and relates to a hydraulically driven vehicle equipped with one or more hydraulic motors for driving an axle or respective axles, and provided with one or more bypass valves each of which bypasses between suction and delivery ports of each of the hydraulic motors.
2. Related Art
As disclosed in U.S. Pat. Nos. 6,732,828 and 6,845,837, there is a conventional, well-known hydraulically driven vehicle equipped with respective hydraulic motors for front and rear axles. The hydraulic motors are provided with respective bypass valves each of which is to be opened for bypassing fluid between the suction and delivery ports of each of the hydraulic motors. When the vehicle is hauled, an operator performs the operation for opening the bypass valves so as to bypass fluid between the suction and delivery ports of each of the hydraulic motors and drain the fluid to a fluid sump, thereby allowing the hydraulic motors to act as pumps driven by the rotating axles regardless of a hydraulic pump fluidly connected to the hydraulic motors. The operation for opening the bypass valves is also performed for fluid connection of hydrostatic transaxles including the respective hydraulic motors or for releasing air during exchanging of fluid.
However, it may happen that an operator forgets to close one or more of the bypass valves after the need for opening the bypass valves has passed. Unclosed bypass valves cause inactivation of the corresponding hydraulic motor, thereby resulting in unstable travel of the vehicle because of a difference in rotary speed between the front and rear axles. Further, in the case that the hydraulic motors are fluidly connected to the hydraulic pump in series and the bypass valve of the upstream hydraulic motor is not closed, the downstream hydraulic motor is also inactivated, i.e., both of the hydraulic motors are inactivated, whereby the vehicle cannot travel.
Further, during traveling of the vehicle, an unclosed bypass valve causes insufficient dynamic braking action of the hydraulic pressure of the fluid delivered from the hydraulic pump, thereby preventing the vehicle from being properly decelerated or braked.
Further, the fluid drained from an unclosed bypass valve increases pressure of the fluid sump in a transaxle housing incorporating the corresponding hydraulic motor, thereby causing leakage of the fluid from the transaxle housing. Consequently, in the past the transaxle housing has been expensively sealed against such an unexpected leak of fluid.